System and methods to determine and monitor changes in microstructural properties

ABSTRACT

A system and methods with which changes in microstructure properties such as grain size, grain elongation, texture, and porosity of materials can be determined and monitored over time to assess conditions such as stress and defects. An example system includes a number of ultrasonic transducers configured to transmit ultrasonic waves towards a target region on a specimen, a voltage source configured to excite the first and second ultrasonic transducers, and a processor configured to determine one or more properties of the specimen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 12/079,925, filed Mar. 28, 2008, entitled “System and Methods toDetermine and Monitor Changes in Microstructural Properties,” whichclaims priority to U.S. Provisional Application No. 60/920,991, filedMar. 30, 2007, entitled “Detection System and Methods,” and which is acontinuation-in-part application of U.S. application Ser. No.11/724,025, filed Mar. 14, 2007, entitled “Systems and Methods toDetermine and Monitor Changes in Rail Conditions Over Time,” whichclaims priority to U.S. Provisional Application No. 60/782,608, filedMar. 15, 2006, entitled “Systems and Methods for Monitoring LongitudinalStress in Rail,” all of which are incorporated herein by reference intheir entirety for all purposes.

This invention was made with government support under DRFR53-04-G00011awarded by the Federal Railroad Administration and DE-FG02-01ER45890awarded by the Department of Energy. The government has certain rightsin the invention.

TECHNICAL FIELD

The present invention relates generally to a system and methods withwhich changes in microstructural properties such as grain size, grainelongation, texture, and porosity of materials can be determined andmonitored over time to assess conditions such as stress and defects.

BACKGROUND

For purposes of this application, the present invention is discussed inreference to polycrystalline materials, but the present invention isapplicable to any heterogeneous material such as paracrystallinematerials. A polycrystalline material is a material that is made ofmicrostructure comprising many smaller crystallites, or grains, withvarying orientation. The variation in direction of the grains, known astexture, can be random or directed depending on growth and processingconditions. The grains also vary in size, deformation (elongation), andvoid spaces between grains, or porosity.

A polycrystalline material includes almost all common metals and manyceramics. A polycrystalline material is a structure of a solid, forexample, steel or brass, that when cooled form liquid crystals fromdiffering points within the material.

One example of a polycrystalline material is steel. For exemplarypurposes, the present invention is discussed in reference to steel inthe form of railroad rail, but the present invention is applicable toany material in any form or size or shape for which material propertiesare desired to be determined and monitored over time such as to assessconditions of stress and defects.

Rail is used on railways, otherwise known as railroads, which guidetrains without the need for steering. As shown in FIG. 1, rail tracks 20typically consist of two parallel rails 22, 23. Rails are typically madefrom steel, which can carry heavier loads than other materials. Rails22, 23 are laid upon cross ties 24 that are embedded in ballast 26.Cross ties 24, also known as sleepers, ensure the proper distance, orgauge, between the rails 22, 23. Cross ties 24 also distribute the load,or force, on the rails 22, 23 over the ballast 26. Plates 28 arepositioned on top of cross ties 24 to receive rails 22, 23. The rails22, 23 are then fastened to the cross ties 24 by a fastener 30, forexample, with rail spikes, lag screws, bolts, or clips. The fastener 30is driven through the plate 28 and into the cross tie 24.

Shown in FIGS. 2 and 3 is a representative rail 22. Rail 22 consists ofrail sections 22′, 22″. Rail sections 22′, 22″ can be aligned andsecured together by joint bars 32 (FIG. 2) or welding 34 (FIG. 3). Mostmodern railways use welding to align secure rail sections, known ascontinuous welded rail (“CWR”), to form one continuous rail that may beseveral miles long. In this form of track, the rails are welded togethersuch as by thermite reaction or flash butt welding.

Longitudinal stress is a problem over large regions of rail track.Stress is a measure of force per unit area, typically expressed inpound-force per square inch (psi). The term “longitudinal” means “alongthe major (or long) axis” as opposed to “latitudinal” which means “alongthe width”, transverse, or across.

Longitudinal rail stress (“LRS”) is usually related to rail contractionsand expansions due to changes in temperature. Longitudinal rail stressleads to failure, which is loss of load-carrying capacity. Examples offailure include, for example, buckling and fracture. Rail experiencestensile stress in cold temperatures, which can lead to fracture orseparation of a rail into two or more pieces. In hot temperatures railexperiences compression stress, which can lead to buckling or warping.Tensile stress is a stress state causing expansion (increase in volume)whereas compression stress is a stress state causing compaction(decrease in volume). It should be noted that a zero stress state iswhen the material does not experience any stress. Failures, among otherthings, cause derailments and service disruption.

The ability to measure longitudinal rail stress is a primary challengein the railway industry. The presence of large regions of rail trackreduces the ability of rail to expand and contract easily due to dailyand seasonal temperature changes. Thus, high longitudinal stresses candevelop, which, in turn, leads to possible failure.

In the United States, from years 2001-2003, there were over 98derailments associated with track buckling. Damage estimates for thesederailments exceed $37 million. In addition, over 900 additionalincidents associated with rail stress were reported. LRS is an on-goingmajor difficulty for railroads.

There has been extensive research to develop a non-destructive method tomeasure LRS. Current techniques include strain gauges (e.g., availablefrom Salient Systems) and rail uplift (e.g., the VERSE system by Vortok,Inc.). There are downfalls to these current techniques. Strain gaugesonly provide measurements related to stress in a local, or confinedarea. Additionally, strain gauges present difficulty in determining thezero stress state. Measurement by rail uplift is costly and requires asection of rail to be detached from the ties. Techniques, such as thesesingle-point measurements, make it difficult to obtain measurements onlarge regions of rail track. Besides steel, a variety of otherpolycrystalline materials may need to be assessed to determine andmonitor microstructural properties over time.

Traditional ultrasonic inspection methods include stress induceddisplacement, angle of incidence, differential pulse transit, pulsecount, and signal relativity. With induced displacement, an ultrasoundwave is introduced into the material using a transducer at a specifiedangle of incidence. The signal is received by an array of sensors at apredetermined spacing a distance from the transmitter after passingthrough and reflected from the bottom surface of the material. Thespacing between the transmitter and receiving sensors is modified by ahydraulic servo-controller to maximize the signal at the centerreceiving sensor. Material height is measured independently in order toquantify the travel distance of the incident wave.

Angle of incidence introduces a longitudinal wave into the top surfaceof the material. The refraction path through the material and reflectedfrom the bottom surface is measured by sensors. The angle of thetransmitting transducer is adjusted to maintain a constant signal at thereceiving sensors. This change in angle is used to determine the stressstates of the material.

Differential pulse transit uses a pair of pulse trains coupled into thematerial. The time difference measured in the equivalent pulses in thepair of pulse trains is then related to the stress state of thematerial. The baseline travel time is based on measurements on stressfree material. Differences in the travel time are indications ofcompressive or tensile stress.

The pulse count method introduces a pulse train into the material. Thepulses are spaced such that the stress states will cause them to overlapor spread in time. The number of pulses is counted to extract the stressstate provided the pulse separation is appropriately chosen.

Two successive sinusoidal waves are introduced into the material withsignal relativity. As the waves propagate, their spacing in time changesbased upon the stress state. This spacing is determined by quantifyingthe amplitude of the received signal relative to the incident waves.

Problems with these methods are that they all require introduction ofthe ultrasonic wave through the top surface of the material andreflection of the incident waves from the bottom surface of the materialwithout considering the microstructural properties of the material.

An improved ultrasonic inspection system and methods are needed for anyand all types of materials regardless of size and shape to assessmicrostructure properties of the material. Determining and monitoringmaterial properties of microstructure over time may lead to specifictypes of processing of these materials in order to reduce or eliminatestress or defects in the material. For example, a specific sequence of aheat treatment process, such as annealing or sintering, may be utilizedto alleviate significant alterations of microstructure duringprocessing.

There is a demand, therefore, for an improved ultrasonic inspectionmethod that is reliable, practical, and cost effective with whichchanges in microstructural properties can be determined and monitoredover time, including conditions related to stress and defects. Thepresent invention satisfies that demand.

SUMMARY

The present invention determines and monitors microstructural propertiesof materials. In one embodiment, the present invention is an ultrasonicinspection system and methods utilizing ultrasonic wave speed. Inanother embodiment, the present invention is an ultrasonic inspectionsystem and methods utilizing scatter of an ultrasonic wave. Utilizingscatter of an ultrasonic wave eliminates exploitation of the subsurfacelongitudinal wave which requires an angle of incidence. Scatter is ageneral physical process whereby propagating waves are forced to deviatefrom a straight trajectory because of non-uniformities in the materialthrough which it passes.

According to the present invention, an improved ultrasonic inspectionsystem and methods utilize scatter of an ultrasonic wave to determineand monitor changes in material properties, such as changes inmicrostructure grain size, grain elongation, texture, and porosity.Microstructural properties of materials can be determined and monitoredover time to assess conditions such as stress and defects. The presentinvention determines and monitors microstructural properties ofmaterials of any size and shape such as planar, cylindrical, andspherical.

For purposes of this application, the present invention is discussed inreference to rail tracks on railways, but the present invention isapplicable to any structure, including geological structures. Forexample, the present invention can determine and monitor changes inconditions of buildings, bridges, fault lines for predictingearthquakes, and land mass for prospecting oil.

In one embodiment, the present invention is directed to a system andmethods with which changes in microstructure properties can bedetermined and monitored over time using scatter of an ultrasonic wave.A transducer holder is positioned on a specimen. For purposes of thisapplication, the term “specimen” is any heterogeneous material for whichconditions such as stress or defects are desired to be determined andmonitored. A transducer holder includes a top surface and a bottomsurface in which a plurality of guides are created. The plurality ofguides extends from the top surface to the bottom surface of thetransducer holder. Each guide is angularly positioned within thetransducer holder with respect to the top surface. A transducer ispositioned within each guide and a voltage source excites an ultrasonicwave to propagate through the specimen. The voltage source may include,for example, a signal generator device or a laser. A laser generatesheat creating an ultrasonic sound wave, whereas one type of signalgenerator device generates electromagnetic waves coupled into ultrasonicwaves. In embodiments that use a laser to generate a signal, the laseris fired at the material, thereby generating heat and an ultrasonic wavewhich may be received by a laser interferometer. As a result, theultrasonic wave is scattered within the specimen. Each transducerreceives a signal from the scattered ultrasonic wave and a digitalsignal processor digitizes the signals. A pulse-echo technique isappropriate when using the same transducer to send and receive anultrasonic wave for embodiments exploiting scatter of an ultrasonicwave.

In a specific embodiment, rail conditions can be determined andmonitored over time using scatter from an ultrasonic wave. In thebroadest form, the present invention includes a transducer holder, avoltage source, an energy conversion device, an electronic test device,a database, a computing device, and a navigation device.

A voltage source, such as a signal generator device, excites a pulsefrom a transducer that is ultimately useful to non-destructively assessmaterial conditions in rail. One embodiment of a signal generator deviceis a pulser-receiver. A pulser-receiver includes a pulser that generatespulses, such as electrical signals, and thereby ultrasonic sound waves,and a receiver to receive them.

The signal generator device introduces a signal into the rail. The angleat which the signal is introduced for rail steel is between a range of 0degrees and 33 degrees. An energy conversion device converts signalsfrom one form to another. One such type of energy conversion device is atransducer, which includes such types as electromagnetic,electrochemical, electromechanical, electroacoustic, photoelectric,electrostatic, or thermoelectric. Transducers typically communicate froma transmitting transducer to a receiving transducer.

One embodiment of the invention includes a system and methods whereinthe energy conversion device is securable to the rail track of arailway. Another embodiment of the invention includes a system andmethods wherein the energy conversion device is securable to a couplingdevice, such as an applicator. The applicator is any homogeneousmaterial that allows the energy conversion device to introduce thesignal at a specific angle to propagate into the rail.

Another embodiment of the invention includes a system and methods inwhich the energy conversion device is securable to the wheels of arailway car to implement a “rolling” system. A “rolling” system allowsthe present invention to become mobile, thereby allowing rail conditionsto be determined and monitored over large regions of rail track. In thisembodiment, a fluid-filled roller is used. The rollers can further housethe energy conversion device, such as a transducer. The energyconversion device is positioned within the roller such that itintroduces the signal into the rail at the desired angle. It is furthercontemplated that a “rolling” system can be integrated with other railmeasurement techniques, or with defect detection vehicles such as thoseused by Sperry Rail Service or Herzog Services, for example.

An electronic test device captures data, such as voltage, current,ultrasonic wave information, temperature, date, time, position, or anymeasurement just to name a few. Such equipment may include an infraredtemperature detector, Global Positioning System (“GPS”), voltmeter,ohmmeter, ammeter, power supply, signal generator, pulse generator,oscilloscope, and frequency counter, for example. Ultrasonic waveinformation can include scatter, speed, amplitude, and wavelength.

A computer system is used to calculate and store data. The computersystem may be remote from, or integrated with, the ultrasonic inspectionsystem. The computer system allows for real-time data analysis. Acomputer system is a machine for manipulating data according to a listof instructions. For example, a computer can be a laptop computer,handheld device, or personal digital assistant.

With embodiments using scatter of an ultrasonic wave, a computerprocessor calculates a spatial variance value from the measured signalsreceived by the transducer. A computer database analyzes the value bycomparing the calculated spatial variance to a theoretical spatialvariance value to assess changes in microstructure properties. Thetheoretical spatial variance value is stored in the database as a firstset of data. The database may further store the calculated spatialvariance values as a second set of data. It is contemplated that thefirst set of data or second set of data is historical data taken overtime at the same location on the specimen. Various calculations can beperformed on the first set of data and second set of data, such as anaverage of one set of data or a comparison between both sets of data.

With embodiments using speed of an ultrasonic wave, a computer processoruses an autocorrelation component to calculate the wave speed from themeasured signals received by the transducer.

The present invention also includes a database for the storage of agrouping of data. A grouping of data can include one or more sets ofdata. One or more sets of data can be compared with other one or moresets of data, as well as utilized for various calculations. For example,a first set of data can be compared with a second set of data. Likewise,data can be computed and analyzed, for example, to determine the stressstate or defects in a specimen. The database can be retained on acomputer used to conduct much of the analyses or retained on a separatecomputer or computing device, or even an on-board or integrated computersystem.

Data includes, for example, location measurement such as from a GlobalPositioning System (“GPS”), wave speed, temperature, and the grain size,grain elongation, texture, and porosity of materials. It is furthercontemplated that baseline data can be established for comparison withthe grouping of data. The baseline data can be, for example,“stress-free” or “zero” measurements. If baseline data is notestablished, one grouping of data can be compared to another grouping ofdata. The database may also include acoustoelastic constants, which areproperties of a material that correlate changes in wave speed to changesin stress or defects.

In one example, the improved system and methods of the present inventionpermit changes in rail conditions, most specifically longitudinal railstress, to be assessed and monitored over time dynamically andnondestructively. One embodiment of the system includes a signalgenerator device that generates a signal that is transmitted to anenergy conversion device. The energy conversion device converts thesignal to a sound wave that propagates through the rail and is returnedto the energy conversion device. The navigation device determinesposition of the sound wave at specific time intervals. A navigationdevice is a device with position or location capability, such as aGlobal Positioning System (“GPS”). An electronic test device capturesthis data and stores the data to a database.

In embodiments using scatter, the computing device processes the datapertaining to microstructural properties such as grain size, grainelongation, texture and porosity, which govern the scatter of theultrasonic wave. The ultrasonic wave is associated with longitudinal andshear wave scattering manifested through spatial variance.

In embodiments using wave speed, the computing device processes the datapertaining to position of the sound wave at specific time intervals tocompute wave speed. The computer system analyzes waves, such aslongitudinal, shear and Lamb waves. The wave speed at specific intervalsof time as a function of position is also stored in the database forcomparison to previous or subsequent data to determine and monitorchanges in rail conditions.

According to the present invention, increasing wave speeds indicates anincrease in longitudinal rail stress potentially leading to rail breakswhile decreasing wave speeds indicates a decrease in longitudinal railstress potentially leading to rail buckling.

The present invention has an objective of providing a system and methodsto determine and monitor changes in microstructural properties such asgrain size, grain elongation, texture, and porosity of materials toassess conditions such as stress and defects.

The present invention has another objective of providing a system andmethods to determine and monitor changes in material microstructure suchas rail conditions, including conditions related to stress and defects.

Another object of the present invention is to exploit ultrasonic wavesat high frequencies, such as frequencies greater than 10 Megahertz,although any frequency is contemplated.

Another object of the present invention is to measure rail stress overlarge regions of rail track to mitigate stress-related issues, such asfractures and buckling.

The present invention increases rail track safety by predicting failuresbefore they occur.

Another object of the present invention is to provide a system andmethods for rail track maintenance.

While current technology is focused on single-position measurements, thepresent invention provides multiple position measurements of stress inrail.

Another object of the present invention is to provide a database formass storage of data. The database can be accessed for analysis of thedata including various calculations to determine and monitor changes inrail conditions over time.

Another object of the present invention is to utilize a navigationsystem to accurately determine position of the failure.

These and other advantages, as well as the invention itself, will becomeapparent in the details of construction and operation as more fullydescribed and claimed below. Moreover, it should be appreciated thatseveral aspects of the invention can be used in other applications wheremonitoring of stress would be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates rail tracks;

FIG. 2 illustrates rail tracks aligned and secured together by jointbars;

FIG. 3 illustrates rail tracks aligned and secured together by welding;

FIG. 4 is a block diagram for determining and monitoring microstructuralproperties utilizing ultrasonic wave speed according to the presentinvention;

FIG. 5 is a block diagram for determining and monitoring microstructuralproperties utilizing scatter of an ultrasonic wave according to thepresent invention;

FIG. 6 is a block diagram of a general computer system according to thepresent invention;

FIG. 7 illustrates an embodiment of the present invention, a transducerholder for use with a planar specimen;

FIG. 8 illustrates an embodiment of the present invention, a transducerholder for use with a cylindrical specimen;

FIG. 9 illustrates a system for determining and monitoring stress inrail according to the present invention; and

FIG. 10 illustrates the measurements taken from the system of FIG. 9.

DETAILED DESCRIPTION

The present invention will now be described in detail with reference tocertain embodiments thereof as illustrated in the accompanying drawings.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention andhow it may be applied. It will be apparent, however, to one skilled inthe art, that the present invention may be practiced without some or allof these specific details. In other instances, well-known process stepsand/or structures have not been described in detail to preventunnecessarily obscuring the present invention.

An embodiment utilizing ultrasonic wave speed of the system and methodsof the present invention are illustrated as a block diagram 100 in FIG.4. In this embodiment, a pulser-receiver 110 generates an electricalsignal that is transmitted 113 to a transducer 122. The transducer 122converts the electrical signal to an ultrasonic wave 115 that propagatesthrough the rail 180 to a receiving transducer 124. The GPS 130determines position of the sound wave 115 at specific time intervals. Anoscilloscope 140 captures measurements of data transmitted 117, such asultrasonic wave information, temperature, date, time, and position, andprovides the data via transmission 119 to the computer 150 forprocessing. The computer 150 can further include a database 160 forstorage of the data.

In another embodiment, a laser is used to generate a signal by firingthe laser at a rail, thereby generating heat and an ultrasonic wavewhich may be picked up by a receiving transducer 124.

The computer 150 may include an autocorrelation component forembodiments of the present invention that utilize wave speed tocorrelate changes in wave speed to changes in stress or defects. Anautocorrelation component assists in calculating the travel time of theultrasonic wave. The travel time is then used to calculate theultrasonic wave speed. If the initial electrical signal generated fromthe transducer 122 includes a set of voltages V_(i) at times t_(i), thenthe autocorrelation formula is defined as:

${r_{k} = \frac{\sum\limits_{i = 1}^{N - k}{\left( {V_{i} - \overset{\_}{V}} \right)\left( {V_{i + k} - \overset{\_}{V}} \right)}}{\sum\limits_{i = 1}^{N}\left( {V_{i} - \overset{\_}{V}} \right)^{2}}},{{{where}\mspace{14mu}\overset{\_}{V}} = {\frac{1}{N}{\sum\limits_{i = 1}^{N}{V_{i}.}}}}$

Maxima in the vector r determines the travel times, otherwise referredto herein as the speed, of the ultrasonic wave. The travel times aredictated by the peak(s) of the ultrasonic wave (see FIG. 10). This datais stored in the database 160 and used for comparison with othermeasurements (baseline, past or subsequent).

The computer utilizes the autocorrelation formula to calculate the wavespeed of the ultrasonic sound wave. The wave speed is calculated bydividing transducer separation distance by the travel time of the soundwave. This wave speed data, along with other data such as temperature,date, time, and position of the sound wave at specific intervalsdetermined by the navigation device, are stored onto a database 160.

FIG. 5 is a block diagram 200 for determining and monitoringmicrostructural properties utilizing scatter of an ultrasonic waveaccording to the present invention. In this embodiment, a voltage source210 generates an electrical signal that is transmitted 213 to excitetransducer 222. The transducer 222 converts the electrical signal to anultrasonic wave 215 that propagates through the specimen 280. Theultrasonic wave 215 is also received by transducer 222 utilizing apulse-echo technique. It is further contemplated that a GPS 230 maydetermine position of the ultrasonic wave 215 at specific timeintervals. A digital signal processor 240, for example, an oscilloscope,captures transmitted 217 data from the ultrasonic wave such as grainsize, grain elongation, texture, and porosity. Temperature may bemeasured independently using, for example, an infrared temperaturedetector. The digital signal processor 240 provides the data viatransmission 219 to the computer 250 for processing. Numerous signalsare used to calculate a spatial variance value. The spatial variance iscalculated to determine changes in the microstructure.

The spatial variance of the signals is calculated by first determiningthe spatial average:

${b(t)} = {\frac{1}{M}{\sum\limits_{i}^{M}{V_{i}(t)}}}$

where M is the number of positions and V_(i)(t) is the measured signalat position i. The spatial variance is defined as:

${n(t)} = \sqrt{\frac{1}{M}{\sum\limits_{i}^{M}\left( {{V_{i}(t)} - {b(t)}} \right)^{2}}}$

and is determined on a computer or other signal processing board. Thisspatial variance represents a measure of the microstructure state in thespecimen. Changes in the microstructure are determined by examining howthe theoretical spatial variance differs from the measured value used todetermine the stress state in the sample.

The computer 250 can further include a database 260 for storage of thedata.

The data stored within the database 260 includes grain size, grainelongation, texture, and porosity at specific intervals of time as afunction of position. Data also includes grain size, grain elongation,texture, and porosity which can be determined from changes in wavespeed. This data is compared to a grouping of data stored within thedatabase 260 to determine and monitor changes in the condition of thespecimen 280.

FIG. 6 is a block diagram showing the structure of a general computersystem 150 according to the present invention. The system 150 includes acentral processing unit (CPU) 151, a read-only memory (ROM) 152, arandom access memory (RAM) 153, a processor 155, and a database 160, allinterconnected by a system bus 154. The database 160 serves as a storagedevice and may further include data 161.

FIG. 7 illustrates an embodiment of the present invention, transducerholder 320, for use with a planar specimen of a polycrystallinematerial. This embodiment is designed for measurements on planar or flatspecimens such as plates, beams, and rails to name a few. The transducerholder 320 is made from any homogeneous material, such as plexiglass,and includes a top surface 321 and a bottom surface 322. The transducerholder 320 has at least two guides 350, wherein the guide extendsthrough the top surface 321 and bottom surface 322 of the transducerholder 320. The guides 350 are oriented at specific angles between andincluding zero to thirty degrees with respect to the top surface 321. Asshown in FIG. 7, the guides 350 are cylindrical through-holes 351,although any sized or shaped guides are contemplated.

The guides 350 act as channels for placement of the transducers 122 (or222). A voltage source (not shown) excites the transducers 122 (or 222)to propagate ultrasonic waves. Ultrasonic waves travel through acoupling medium, such as air, water, glycerine, or any viscous fluid inthe specimen. Each transducer 122 (or 222) then receives a signal afterthe wave returns. The signal is then digitized and placed in apulse-echo technique. A pulse-echo technique is appropriate when usingthe same transducer 122 (or 222) to send and receive an ultrasonic wave.Numerous signals are used to calculate on a spatial average value.Spatial averaging is calculated to determine changes in themicrostructure of a specimen. It is desirable to collect the numeroussignals by moving the transducer holder 320 to various positions on thespecimen. Typically each position is at least 0.5 mm away from the otherpositions and at least 20 positions are needed to have a relativelysmooth result.

FIG. 8 illustrates an embodiment of the present invention, transducerholder 330, for use with a cylindrical specimen of a polycrystallinematerial. This embodiment is designed for measurements on cylindrical,or curved, specimens such as packaging or a pressure vessel. Thetransducer holder 330 is made from any homogeneous material, such asplexiglass, and includes a top surface 331 and a bottom surface 332.Again, transducer holder 330 is placed on the specimen for whichmicrostructure properties are desired. The transducer holder 330 has atleast two guides 350, wherein the guide extends through the top surface331 and bottom surface 332 of the transducer holder 330. The guides 350are oriented at specific angles between and including zero to thirtydegrees with respect to the top surface 321. As shown in FIG. 8, theguides 350 are cylindrical through-holes 352 although any sized orshaped guides are contemplated.

Transducers 122 (or 222) are placed within the guides 350 and a voltagesource (not shown) excites the transducers 122 (or 222) to propagateultrasonic waves. Each transducer 122 (or 222) then receives a signalafter the wave returns, which is then digitized.

FIG. 9 illustrates an embodiment of a system 500 for determining andmonitoring stress in rails according to the present invention. Atransducer 122 and receiving transducer 124 are sized and shaped suchthat each may be positioned on a surface of the rail 25 such as a sidesurface 25A, or top surface 25B of a rail 25 through a coupling device27, such as applicator. In embodiments that use scatter of an ultrasonicwave, the transducer 122 receives the ultrasound wave scatter withoutthe need for transducer 124.

The coupling device 27 may be in the form of a wedge or other shape topermit easy adherence to the rail surface 25A, 25B. The coupling device27 is preferably formed of a material to facilitate the transmission ofthe ultrasonic wave by the transducer 122 and the receptor of theultrasonic wave by the receiving transducer 124. Acrylic is one of themany materials that may be used for this purpose. Other embodiments ofthe system and methods utilize the positioning of the transducers 122,124 on the wheels of a railway car.

With reference to FIG. 9, embodiments that use scatter of an ultrasonicwave include a voltage source 110 that sends a voltage signal to thetransducer 122. The transducer 122 converts the voltage signal to anultrasonic sound wave that propagates through the rail 25 and isreceived by transducer 124. The transducer 122 amplifies and digitizesthe sound wave into signals. The signals received from the transducer122 may be acquired such as with an oscilloscope 140 and conveyed to adatabase, for example, within a laptop or equivalent computer (notshown). The database is used for data analysis of the signals. Thecomputer utilizes an autocorrelation formula to calculate the traveltime of the sound wave. The wave speed is then calculated by dividingtransducer separation distance by the travel time of the sound wave.

This wave speed data, along with other data such as temperature, date,time, and position of the sound wave at specific intervals determined bythe navigation device, are stored in a database. Again, in embodimentsthat use ultrasonic wave scatter, the computer calculates a spatialvariance value. This spatial variance data, along with other data suchas grain size, grain elongation, texture, and porosity, are stored intothe database. Data such as temperature can be taken by the transducers122, 124 on the rail 25. Likewise, the navigation device (not shown) cantake the position data at the location where the temperature data istaken.

The database 160 may store the data at specific intervals of time as afunction of position. The database 160 can be on the computer 150 or ona separate computer.

The computer 150 compares data of the database 160. A first set of datacan be compared to other sets of data. The first set of data can be onedata point, a plurality of data points, a base line or control datapoints. A second set of data points can be one data point or a pluralityof data points for comparison with the first set of data points. Thecomparison between data points determines abnormalities or changes, ifany, between the data over time. The database would store theoreticalspatial variance values as well as historical values measured at thesame location for comparison.

According to the present invention, a first set of data points, such asspatial variance, is compared to a second set of data points. Acomparison resulting in an increase in wave speeds indicates an increasein longitudinal rail stress potentially leading to rail breaks while acomparison resulting in a decrease in wave speeds indicates a decreasein longitudinal rail stress potentially leading to rail buckling.

While endeavoring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicants claim protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon. While the apparatus and method hereindisclosed forms a preferred embodiment of this invention, this inventionis not limited to that specific apparatus and method, and changes can bemade therein without departing from the scope of this invention, whichis defined in the appended claims.

Therefore, the foregoing is considered as illustrative only of theprinciples of the invention. Further, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and operationshown and described, and accordingly, all suitable modifications andequivalents may be resorted to, falling within the scope of theinvention.

What is claimed is:
 1. A system for analyzing stress in apolycrystalline specimen, comprising: a. a first ultrasonic transducerconfigured to transmit a first ultrasonic wave at a first angle ofincidence towards a target location on a specimen; b. a secondultrasonic transducer configured to transmit a second ultrasonic wave ata second angle of incidence towards the target location on the specimen;c. a voltage source configured to excite the first and second ultrasonictransducers, wherein each transducer is configured to operate inpulse-echo mode to receive a scattered ultrasonic signal from thespecimen in response to the first and second ultrasonic waves; d. aprocessor configured to calculate a statistical spatial variance valuefrom the plurality of scattered ultrasonic signals as a function ofspatial position, wherein the scattered ultrasonic signal received bythe first and second transducers comprises both longitudinal and shearwaves; and e. database of theoretical spatial variance values whereinsaid statistical spatial variance values for the longitudinal and shearwaves are compared to the theoretical variance values to assess changesin microstructure properties of the specimen over time.
 2. The system ofclaim 1, wherein the microstructural properties assessed include grainsize, grain elongation, texture, and porosity at specific intervals oftime as a function of position.
 3. The system of claim 2, wherein themicrostructural properties are determined as a function of wavespeed. 4.The system of claim 3, wherein the spatial variance of the signals iscalculated by first determining the spatial average.
 5. The system ofclaim 4, wherein the processor further comprises an autocorrelationcomponent configured to utilize wave speed to correlate changes in wavespeed to changes in stress or defects.
 6. The system of claim 5, furthercomprising a transducer holder comprising a plurality of guides coupledto the transducer holder, each guide configured to receive acorresponding ultrasonic transducer.
 7. The system of claim 6, whereinthe specimen is a rail, and wherein the transducer holder is configuredto move along the rail.
 8. The system of claim 7, wherein the transducerholder comprises a fluid-filled roller.
 9. The system of claim 6,wherein the transducer holder is cylindrically shaped.
 10. The system ofclaim 1, further comprising a navigation device configured to determineposition information of the first and second ultrasonic waves atspecific time intervals.
 11. A system for analyzing stress in the grainsof a rail, comprising: a. a first ultrasonic transducer configured totransmit a first ultrasonic wave at a first angle of incidence towards atarget location on a rail; b. a second ultrasonic transducer configuredto transmit a second ultrasonic wave at a second angle of incidencetowards the target location on the rail; c. excitation means for pulsingthe first and second transducers, wherein each transducer operates inpulse-echo mode and is configured to receive a scattered ultrasonicbackscatter signal from the rail in response to the first and secondultrasonic waves; d. processing means for calculating a statisticalspatial variance value from the scattered ultrasonic signals as afunction of spatial position and comparing the spatial variance value toone or more theoretical spatial values over time: and e. determiningstress by assessing microstructural properties of the grains of the railat specific intervals of time as a function of position.
 12. A devicefor analyzing a polycrystalline specimen, comprising: a. a means forexciting a plurality of ultrasonic transducers to operate in pulse-echomode to transmit multiple ultrasonic waves to a target location on aspecimen; b. a means for digitizing scattered ultrasonic signalsreceived from the specimen in response to the ultrasonic waves; c. ameans for calculating a statistical spatial variance value from theultrasonic backscatter signals as a function of spatial position; and d.a means for comparing the spatial variance value to a theoreticalspatial variance value stored in a database to assess a change in one ormore properties of the grains of the polycrystalline specimen.
 13. Thesystem of claim 11, wherein the microstructural properties assessedinclude grain size, grain elongation, texture, and porosity at specificintervals of time as a tinction of position.
 14. The system of claim 13wherein the microstructural properties are determined as a function ofwavespeed.
 15. The system of claim 14, wherein the spatial variance ofthe signals is calculated by first determining the spatial average. 16.The system of claim 15, wherein the processing means further comprisesan autocorrelation component configured to utilize wave speed tocorrelate changes in wave speed to changes in stress or defects.
 17. Thesystem of claim 13, further comprising a transducer holder comprising aplurality of guides coupled to the transducer holder, each guideconfigured to receive a corresponding ultrasonic transducer.
 18. Thesystem of claim 17, wherein the transducer holder is configured to movealong the rail.
 19. The system of claim 17, wherein the transducerholder comprises a fluid-filled roller.
 20. The system of claim 17,wherein the transducer holder is cylindrically shaped.